Re: new heapcheck contrib module

> On Aug 27, 2020, at 10:07 PM, Andrey M. Borodin <x4mmm@yandex-team.ru> wrote:
>
>
>
>> 25 авг. 2020 г., в 19:36, Mark Dilger <mark.dilger@enterprisedb.com> написал(а):
>
> Hi Mark!
>
> Thanks for working on this important feature.
>
> I was experimenting a bit with our internal heapcheck and found out that it's not helping with truncated CLOG anyhow.
> Will your module be able to gather tid's of similar corruptions?
>
> server/db M # select * from heap_check('pg_toast.pg_toast_4848601');
> ERROR:  58P01: could not access status of transaction 636558742
> DETAIL:  Could not open file "pg_xact/025F": No such file or directory.
> LOCATION:  SlruReportIOError, slru.c:913
> Time: 3439.915 ms (00:03.440)

The design principle for verify_heapam.c is, if the rest of the system is not corrupt, corruption in the table being
checkedshould not cause a crash during the table check. This is a very limited principle.  Even corruption in the
associatedtoast table or toast index could cause a crash.  That is why checking against the toast table is optional,
andfalse by default. 

Perhaps a more extensive effort could be made later.  I think it is out of scope for this release cycle.  It is a very
interestingarea for further research, though. 

—
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company